German Patent specification No. 3 234 027 discloses an apparatus for making and breaking connections between screw threaded tubular members which comprises a rotatable and a non-rotatable chuck disposed along a common axis. The chucks each receive a respective one of two tubular members having male and female screw threaded zones. One chuck is mounted in a bearing block borne rigidly at one end of a frame while the other chuck is disposed on a support block. The apparatus is unwieldy and unsuitable for the performance of the entire screwing process.
German Patent specification No. 2 726 472 discloses the use of pipe tongs having a casing which is formed with a radial cutaway portion adapted to receive a pipe. Disposed in the casing with provision for pivoting by means of a drive system is a toothed rim which is also formed with a matching radial cutaway portion and is provided with cam means having cam surfaces of different pitches. This device is quite suitable for the screw threaded connection of casings which are of substantially uniform diameter. However, drill strings are subject to considerable wear in use. For this reason the pipe diameters in a drill string differ considerably. Furthermore, the breaking of screw threaded connections of drill strings can require very high torques. The open tongues, as disclosed in German Patent specification No. 2 726 472, are not suitable for use with drill strings because of the considerable torques required and the variation in the diameter of the drill string.
It is an object of the invention to provide an apparatus which can be used to make and break screw threaded connections in drill strings and which can be used on a drilling rig.
It is a further object to make such apparatus lightweight so that is can be easily handled.